<div id="field_dropdowns">
  <% @report.fields.each do |field| %>
    <%= fields_for("report_report[fields_attributes][]", Report::Field.new) do |f| %>
      <div>
        <%= f.select(:full_id, grouped_options_for_select(Report::Field.select_options, field.full_id), :include_blank => true) %>
        <a href="#" class="remove_field">Remove</a>
      </div>
    <% end %>
  <% end %>
</div>
<a href="#" class="add_field">Add</a>